1. Field of the Invention
The present invention relates to a numerical control apparatus and a numerical control method for controlling a machine tool, and more particularly to a numerical control apparatus and a numerical control method for controlling a machine tool which machines prototypes or the like.
2. Background Description of the Related Art
Advances in the technology of numerically controlled machine tools have been so great that they can machine workpieces of complex shape at high speed with precision. At present, workpieces of complex shape cannot be machined without numerically controlled machine tools.
To generate machining programs, there are widely used interactive numerical control apparatus which comprise a numerical control apparatus with an interactive program generating function, and automatic programming apparatuses for simply generating complex machining programs.
In the use of such numerical control apparatuses, it is necessary to accurately define machine coordinates, a machine origin, program coordinates, a machining origin, and other data for generating strict machining programs. Although the interactive numerical control apparatus and the automatic programming apparatus can be used to machine a number of workpieces, for some machining processes for producing a prototype or a model, general-purpose milling machines, lathes and the like are used which require a short period of time to carry out preparatory action such as attachment and detachment of workpieces, installation of tools, etc. these processes, and do not require machining programs to be generated.
Problems of general-purpose machine tools are that the number of available operators who can handle general-purpose machine tools is becoming smaller, and it is difficult for the general-purpose machine tools to carry out oblique linear machining, arcuate machining, or the like though they can effect linear machining without any problem.
If, on the other hand, a general numerically controlled machine tool is used to machine a prototype or a model, then it is necessary to accurately define machine coordinates, a machine origin, program coordinates, a machining origin, and other data. While it is not impossible to define those data, the required programming process is too time-consuming and troublesome for machining a portion of a single workpiece.
To solve the above problems, the applicant has filed Japanese Patent Application No. 4-231836 on a numerical control apparatus which employs a general-purpose machine tool for carrying out simple machining processes to machine prototypes or the like.
When a simple machining of prototypes or the like is carried out, however, the machining is usually carried out while sequentially confirming machining processes by operating a manual pulse generator or jog feed buttons. Therefore, although it is possible to move a tool in a direction parallel to any one of an X-axis, a Y-axis and a Z-axis by operating the manual pulse generator or the jog feed buttons, it is difficult to move the tool along an oblique straight line, circular arc or the like by simultaneously driving two or more axes by hand.
It is also difficult to move a tool to a machining start point by moving it with respect to two or more axes along a designated shape such as an oblique straight line, circular arc or the like.
Further, when a simple machining of prototypes or the like is carried out while sequentially confirming machining processes by operating the manual pulse generator or the jog feed buttons, a distance between a designated shape such as a defined oblique straight line, circular arc or the like and the present position of a tool is unknown. As a result, it is difficult to cause the tool to approach the designated shape by operating the manual pulse generator or the jog feed buttons.
In such a numerical control apparatus, a tool is caused to approach a workpiece by operating the manual pulse generator or the jog feed buttons until the tool reaches the vicinity of a cutting start point. When the tool is caused to come into contact with the workpiece carelessly, however, a problem arises in that a cutter mark is formed to the workpiece and the workpiece is machined badly. This is a serious problem when the workpiece is subjected to a finish machining.